In DE-B-3907953.8, DE-B-4112972.5, DE-B-4112968, DE-B-41129695 and U.S. Pat. No. 4,491,628, there have been disclosed radiation-sensitive mixtures which comprise a compound capable of generating an acid by the exposure to radiation, a water-insoluble but aqueous alkaline solution-soluble binder, and a compound which causes a cross-linking reaction (negative-type) or a decomposition reaction (positive-type) in the presence of an acid. These mixtures generate an acid upon exposure to radiation and, after the exposure, heat-treated to cause components thereof to be cross-linked with each other (negative-type) or decomposed (positive type) by catalytic effects of the acid generated to increase the difference in solubility to an aqueous alkaline solution between exposed and unexposed area thereof, thereby producing micro-patterns.
Although the conventional radiation-sensitive mixtures have a sensitivity and resolution sufficient to produce fine semiconductors, there arises a problem that the sensitivity and the definition thereof becomes deteriorated as the period between the exposure and a post-exposure baking step is prolonged. It is suggested that this problem is caused due to the fact that the acid generated by the exposure to radiation is diffused from the exposed area to the unexposed area, thereby rendering acid-latent images produced by the exposure unstable. In general, resist mixtures are required to be kept stable for the period between the exposure and the post-exposure baking step, e.g., for about two hours in the case of the production of semiconductors or for about twenty-four hours in the case of the production of optical masks.